Resistance in series with electrodes



June 13,1933.

H. A. WINTERMUTE I RESISTANCE IN SERIES WITH ELECTRODES Filed May 181927 3 Sheets-Sheet l gwucmtoo fid/w 24.41%

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June 13, 1933. H. A. WiNTERMUTE RESISTANCE IN SERIES WITH ELECTRODE-SFiled May 18, 1927 3 Sheets-Sheet 2 gwwmtoi MM], A MW June 13, 1933- H.A. WINTERMUTE RESISTANCE IN SERIES WITH ELECTRODES Filed May 18, 1927 3Sheets-Sheet 3 i] A MM @MMW) kmuwt;

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Patented June 13, 193

HARRY A. WINTERMUTE, OF PLAINFIELZD, NEW JERSEY, ASSIGNOR T0 RESEARCHPATENT OFFICE CORPORATION, OF NEW YORK,'1\T. Y.,,A CORPORATION OF NEWYORK RESISTANCE IN SERIES W'ITH ELECTRODES Application filed May 18,

' ,This invention relates to the art of electrical precipitation ofmaterials (such as dust, fumes, etc.) suspended in gases.

The precipitation of such materials is effected by passing the gasescontaining them through a high-tension electrical field, in which highelectrical potential difference is maintained between electrodes, thematerial being deposited on such electrodes.

' In practice, it has been found desirable to use a number of electricalprecipitation units connected in multiple. 3

This practice while it enables large volume of gas to be handled hasbeen found to present certain difliculties in that as more units (eachunit consisting of a number of discharge and collecting electrodes) areconnected in multiple, the voltage or potential difference between theelectrodes of each unit has to be lowered, in order to prevent theincreased tendency to are over.

Electrical precipitation systems comprise in general a step-uptransformer, a rectifier to change the alternating current to apulsating direct current which is delivered to the discharge electrodesof the precipitator, through which the gases carrying suspended materialare passing. In this high tension circuit surges, oscillations or tran-.

sient currents may be set up and kept in existence by the pulsationsfrom the rectifier feed, the changing of the gas conditions, the staticcharge in the precipitate, variations in current flow from the coronadischarge points, etc., etc. The precipitator itself has considerableinductance and capacity, which are distributed and tend to foster andaggravate this surging condition.

The larger the units or the more units in parallel, the more pronouncedthis tendency to surging or oscillation is found to be. Suchoscillations may take place between units or different parts of the sameunits and while they may be of small power value, are often just largeenough when superimposed on the main voltage, to cause disruptivedischarges at points where they happen to reach a maximum value.

Furthermore, when such disruptive discharge or arcing occurs, or whenfor any m7. Serial No. 192,376.

other reason a relatively large flow of current occurs at a certainpoint or portion of the precipitator, the voltage is immediately reducedin the remainder of the precipitator, due to the flow of energy fromsuch other portion through the relatively low resistance path at thispoint. This phenomenon, which maybe called localization of theelectrical field, not only results in a waste of electrical power,but-decreases the efficiency of the precipitating action which isdependent upon the maintenance of a high potential difference betweenall portions of the opposing electrodes.

When such conditions exist or arise, it is necessary to reduce theprecipitating voltage in order to prevent such breakdowns, which reducesthe corona discharge, and lowers the percentage of recovery.

It is characteristic of electrical precipitators comprising separatedelectrodes between which a stream of gas is flowing that a smallincrease of voltage above a given discharge point very greatly increasesthe current flow (corona discharge) thereby increasing the efliciency ofthe precipitator. In other words, the gas resistance does not remainconstant, but decreases with increased current flow.

In the usual treater the current flow may be largely localized in arelatively few points in the treater leavin the remainder of the unitpractically ined ective. By the use of resistances or impedances sodistributed as to break up the treater or unit into relatively smallparts isolated from each other by such resistances or impedances andwith resistances or impedances also located in the direct path of thecurrent flow, any tendency to localization due to whatever causeproduces a potential drop in its path partly neutralizing the tendencytowards localization and at the same time the adjoining elements areprevented from pouring their energy into the disturbed area by l theseparating resistance or impedance.

Surges, high frequency oscillations, etc., are primarily generated atthe rectifier and transmitted to theactive treater parts. The connectinglines, insulators, bushings, etc.,

and active parts of the treater including the gas, deposits on thecollecting electrodes, etc, all compose a complex electrical circuitwhich is capable of reflecting 'the surge waves received from therectifier and so producing standing voltage waves within the treater.Such stationary waves occurring in the active treater produce localizedcurrent flow. The resistances or impedances introduced in the circuitbetweenthe active treater parts and the rectifier tend to prevent theestablishment of such standing waves and thus produceuniform-distribution of current flow throughout all parts of the treaterand so maintain every part at maximum efiiciency at all times.

The snapping which ordinarily occurs without producing power arcs isprobably due to the breakdown of these standing Waves, the energydischarged at the time of rupture or in a single snap being only theenergy of the particular wave discharged. However, the discharge of onesuch wave produces disturbances in adjoining or neighboring wavescausing them to break while the original wave is developing its originalpotential. In this manner continual snapping in the treater is developedand the voltage in the treater can only be further increased at theexpense of a further increase in the rate of snapping with enor-' mousincrease of current flow, most of which current is undoubtedly used inthe snapping or in the maintenance of the standing waves.

It is well-known that a small treater, say a single pipe or plate, isfar more eliicient than the results per pipe or plate obtained from agroup of similar units in multiple.

The use of suitable values of resistances or,

impedances in series with both sides of the circuit to each unit(including its discharge electrode).p'roduces a condition of isolationequivalent in some degree to the operation of the units singly.

Therefore this invention has for its main object to provide meanswhereby an increased voltage and the accompanying increased efficiencymay be uniformly and continually maintained at each of a number ofinterconnected electrical precipitation units or elements. A furtherobject of the invention is to prevent or minimize arcing or disruptivedischarge, and to also minimize localization of the electrical field atcertain portions of the precipitator.

These results are attained by subdividing the precipitator system intoas small elements as possible and placing suitable impedances such asresistances, between these elements, by which oscillations andlocalization of the electrical field are practically eliminated.

As each element is small, the amplitudes of the oscillations are smallerthan they would be if they were all in parallel with no preventive meansbetween them. Such oscillations as may tend to arise are promptly dampedor dissipated and preventedfrom reaching harmful values. Furthermore, amon'ientary increase in current flow through any element due to anydisruptive discharge which might occur or to any other cause would inturn produce such a drop in potential across the resistance in serieswith such element as to. immediately lower the potential differencebetween the active portions of such elementsuiiiciently to immediatelysuppress such increased current flow without appreciably lowering thevoltage in other portions of the precipitator.

By thus distributing impedances,etc., in the high tension circuits, thecorona discharge at any element is made substantially independent ofthat from any other, thus enabling more complete and accurate control ofthe system. i

This fundamental idea of providing sufiicient impedances betweenadjoining corona discharges can be applied not only between the units ofan electrical precipitation system, but to other localities in thesystem. in which like conditions of oscillation and localization areliable to occur, and even to the individual discharge electrodes, andexamples of such application of the broad invention are described later.

As has before been pointed out, it is a characteristic of electricalprecipitators that a relatively small increase in voltage may produce arelatively very high increase in corona discharge. As the suspendedparticles in their passage through the precipitator between thedischarge and collecting electrodes are subjected to a greater number ofcorona discharges, a more efiicient separation is eliected.

As the resistance of a precipitator does not remain constant butdecreases with increased current flow, it is said to have negativeresistance characteristics, and as the flow is increased the operationbecomes more unsteady, resulting in arc overs or highly localized"discharges. In some precipitation problems, unless gas conditioning isused, conditions are met in which It is in these cases that ballastingimpedances in series with each corona point are most effective, givingstable current flow and preventing the localization of discharges in arelatively few points. The voltage throughout the precipitator ismaintained at the normal value resulting in an ever. distribution ofcorona discharge, thus maintaining a maximum efiiciency. As resistancesthere may be used wirewound resistances, carborundum rods, orresistances of the semi-conducting type, such as Portland cementconcrete, Transite board or the like. The resistance, through" moistureor precipitate or both, on the surface of insulators or semi-conductingmaterial, may also be utilized.

As a further development of this invention, the use of these resistancesof the semi-conducting type permits the insertion of resistances inclose connection with the discharge electrode supports or collectingelectrode supports, or even with the discharge elements of eachelectrode.

The apparatus used mayl take a great variety of forms, some of w ich areillustrated in the accompanying drawings from which the invention willbe readily understood.

Referring to the drawings:

Fig. 1 is a diagram of a system illustrate ing an embodiment of theinvention;

Figs. 2, 3 and 4 are front elevations of supporting devices for theseries of discharge electrodes;

Figs. 2a, 3a and 4a are corresponding end views;

Figs. 5, 5a, 6 and 6a are elevations and plans of modified forms ofdischarge electrodes;

Fig. 7 is a horizontal section through a modified form of precipitator.

Referring to Fig. 1, P, P are precipitators having discharge electrodes2, 2 and collecting electrodes 3, 3 the discharge electrode beingtensioned by weights W, as is usual. T is a transformer by which thevoltage is stepped up to the required degree, The ends of the secondarycoil are connected through choke coils PC (here indicated as of thepancake type) to two terminals of the rectifier whose other twoterminals tween this beam and the electrode carrying pipes F, F isinterposed a block 0 of highresistance or semi-conducting materialsuchas Transite or concrete. The high ten,- sion connections to the pipes F,F, may be made throu h additional external impedances R, or t eseexternal resistances may be omitted, and the high tension line Bconnected to the supporting beam D, as shown. In this case theresistance of block 0 is interposed in the circuit of each set ofdischarge electrode members.

In Figs. 3 and 3a a pair of conducting the conducting support and eachdischarge electrode.

In Figs. 4 and 4a is shown a modified form in which blocks 7, 7 of hi hresistance material are carried by con ucting supports from the pipes F,the, discharge electrodes 5, 5 belng supported from these blocks.

A still further extension of this invention is possible. In the ordinaryform of continuous conducting discharge electrodes, the points at whichthe corona discharge occurs are haphazardly distributed over theelectrode. By providing definite discharge points, it becomes feasibleto insert ballasting resistances directly at each discharge pointor'group of points.

Thus Figs. 5 and 5a show a discharge electrode comprising a centralconductor 10, on which are arranged hollow blocks 11, having' projectingarms 12 provided with points 13 made of metal or of the block material.The blocks and arms are made of high resistance material, thusinterposing re ulated resistances between the central con uctor and thedischarge points.

A modified arrangement is shown in Figs. 6 and 6a. In this case a flatblock 14 of high resistance material is provided at its edges with'oneor more discharge points 15, 15 and supported by a conducting support asa chain 16. While the points 15 are very desirable, their use is notnecessary, and satisfactory distribution of corona points can be securedwithout the aid of these.

In each of these last two cases, the discharge electrodes are preferablyarranged with their longer dimension parallel to the flow of the gas andbetween the parallel collecting electrodes, as shown in Fig. 7, in whichthe discharge elements, such as those shown in Fig. 6 are shown arrangedbetween parallel collecting electrodes 20, which may be eithervertically arranged metal plates or blocks of semi-conducting materialsuch as concrete.

Some of the advantages of the point construction of discharge electrodesare that alternating current may be used, or the points may be eithernegatively or positively charged. Moreover, if arcing occurs at anypoint, this arcing would not affect the corona discharge at the otherpoints, as is the case when there is no high resistance.

It will thus be noted that the parallel circuits as heretofore used inelectrical precipitation systems are broken up by resistances, whetherthese parallel connected elements are precipitator units, sections ofunits,

smaller groups of discharge electrodes, single discharge electrodes,smaller groups of collecting electrodes, single collecting electrodes ordischarge points on a discharge electrode.

, The improved result in general is that it becomes possible to maintaina current discharge from discharge to collecting electrodes which issubstantially free from currents of an oscillatory or high frequencynature,

This uniformity or evenness of current discharge per unit length ofelectrode permits theuse of higher voltages than can now be safely usedin any of these interconnecte electrical precipitator systems.

The amount of ballasting resistance or other impedance to be used inseries with any unit, section, or electrode, can.not be definitelystated in ohms, since the amount used depends upon a number of factors,among which are the spacing distance between discharge and collectingelectrodes, the kind of gas and the particular character of suspendedprecipitate, the length of the electrodes, etc. Further many types ofhigh tension resistance do not have the same amount of resistance inpulsating rectified currents as they have on high-voltage directcurrents. I

However, according to this invention the resistance or impedances inseries between any two precipitator units, sections, electrodes orpoints must, under all ordinary conditions be suflicicnt to prevent thelocalization of discharges or the cross surges or oscillation betweenthe adjacent elements and, for convenience, resistance or impedances ofthis order are termed surge-resistance impedances or resistances.

It has been the custom to insert resistances in the high tensioncircuits, as for example at the shoes of the rectifier, but theseresistances were small, usually varying from 1000 to 10,000 ohms, Whileaccording to this invention resistances of 100,000 ohms or more areinserted in each of the paralleled leads from the high-tension line tothe precipitators.

It has also been the practice when precipitator units were to beoperated in parallel, to introduce resistance on the low voltage side ofthe transformer. With large size units and a large current flow the useof resistances in the low tension circuit must be minimized to avoidexcessive power losses, and where a short circuit occurs in theprecipitator an excessive rush of current can happen because of thesmall amount of resistance in the high-tension circuit.

When the high resistances are distributed in the manner described, thesedifiiculties are largely obviated.

lhe term element as used in the claims is intended to include a sectionor unit of an electrical precipitator, a set of electrodes in nectingsaid discharge electrodes in parallel to a high-potential source, saidmeans including semi-conductive material interposed between eachdischarge electrode and the high-potential source.

2. In a system for the electrical precipitation of suspended particlesfrom gases a supporting structure, a supporting mem er ofsemi-conducting material mounted on said supporting structure, aplurality of discharge electrode aneans mounted on said semi-conductingsupporting member and connected thereby to said supporting structure, asource of high potential electrical current, and means electricallyconnecting said supporting structure to one side of said current source.

3. In a system for theelectrical precipitation of suspended particlesfrom gases comprising a plurality of. discharge electrodes, a conductivesupporting member therefor and a semi-conductive material interposedbetween said supporting member and said electrodes.

4:. In a system for the electrical precipitation of suspended particlesfrom gases comprising a plurality of discharge electrodes, a con uctivesupporting member therefor and a semi-conductive member interposedbetween said supporting member and said electrodes, said semi-conductivemember serving also to separate said electrodes from each'other.

5. ln an electrical precipitator, a discharge electrode systemcomprising a plurality of discharge electrode elements, semiconductivematerial separating each electrode element from the other electrodeelements, and a conducting member for supplying current to each of saidelectrode elements through said semi-conductix e material.

6. A discharge electrode element comprising a conductive supportingmember, a plurality of spaced conductive discharge points, andsemi-conductive material between each of said discharge points and saidconductive member.

7. A system for the electrical precipitation of suspended particles fromgases comprising collecting electrodes defining a plurality of gaspassages, discharge electrodes opposed to said collecting electrodes forcreating electric fields within said passa es, a source of high voltagecurrent, para lel connections between said current source and thedischarge electrodes in the separate gasv passages, and semi-conductivematerial in the connection to each of said discharge electrodes.

In testimony whereof, I aflix my signature.

' HARRY A. WIN TERMUTEL

